Duramycin is a polycyclic peptide, which increases chloride transport and water mobilization when applied to the apical surface of the airway mucosa. Cystic fibrosis (CF) is a complex inherited disorder that affects children and young adults. Approximately 75,000 patients worldwide suffer from CF. In CF the mutated gene encodes a defective chloride channel. The resulting decreased chloride permeability reduces net water secretion increasing mucus viscosity in the lungs, where mucus plugs the airways and leads to infection. Drugs such as duramycin, targeted to chloride transport, are rational candidates for preventive therapy for CF. The purpose of this project is to test the ability of duramycin to induce chloride secretion in vivo, using potential difference measurements in the nose of normal and CF patients.